The Plaza Restaurant in the MK makes amazing milkshakes -- just real ice cream and milk. They serve it in one of those old fashioned metal mixing containers, and there's plenty to share for two people.
The Plaza is one of those hidden gems - simple food, but really done well and a low key, fun environment.
We love the shakes at Plaza and Prime Time. And the only thing we liked from our entire meal at the Whispering Canyon Cafe was the bottomlesshake (wish they had booze in them because it might have made the meal bearable).
Thanks for all the replies! We'll have to check out one of those places sometime. I haven't been to Sci-Fi or 50's PTC in ages -- may have to give them another try if just for the milkshakes!